1. Field of the Invention
The invention relates to an electronic system, comprising several power-dissipating components, in particular packages containing integrated circuits, and to a method for mounting these components onto a circuit board.
2. Background Art
Circuit boards typically comprise several power-dissipating components (e.g., integrated circuits like processing units, controllers etc., and/or resistors and so on) mounted thereon. Especially integrated circuits (e.g., analog and/or digital circuits, memory devices (PLAs, PALs, ROMs, RAMs, etc.) in the form of silicon chips) can be loaded into and electrically contacted with special housings (“packages”), e.g. made of ceramic, plastic, composite materials and so forth, that may be specifically designed to, amongst other functions, alter and improve the dissipation/spreading of power (typically in the form of heat) of the integrated circuit.
The contact between the integrated circuit(s) and the housing(s) can be achieved by various known means, e.g. soldering, bonding, flip-chip techniques and so on. External contacts of the package (pins, pads, balls etc.) serve to electrically connect one or a plurality of the packages to a corresponding module, in particular, a printed circuit board (PCB). For this purpose, the respective external contacts might e.g. be plugged in or on, and/or soldered to the circuit board. For example, pins might be mounted onto the surface of the board (e.g., in the case of SMD-packages “SMD=surface mounted device”), or might be put into respective connection holes provided in the board (and thereafter, might be soldered).
Many power-dissipating components—and most packages—show an asymmetry in the direction in which they dissipated their power as heat. In particular, we can consider the power dissipated via the top of the package (“PT”), and the power dissipated via the bottom of the package (“PB”). Heat dissipation and power dissipation in this context refer to essentially the same physical effect and could be used interchangeably. For example, some packages are equipped with a built-in heatpad on the bottom side of the package, which results in a higher power dissipation through their bottom than through their top portion, i.e. PB>PT. Other packages are equipped with a built-in heatpad or heatspreader on the top side of the package, which may result in a higher power dissipation through their top side than through their bottom side, i.e. PB<PT.
If, for instance, a package with PB>>PT is soldered on the top side of a printed circuit board (PCB), most of the heat produced by the integrated circuit provided in the package will flow into the printed circuit board (PCB). Further (particularly, if non-thermal vias are used), most of the heat will then flow to the bottom side of the printed circuit board (PCB) from where it will flow away by “natural” and/or “forced” convection (e.g., convection supported by fans).
In the case of a relatively high number of identical packages as just described being soldered to the top side of a printed circuit board (PCB), the total heat flow to the bottom side might become substantial.
Hence, the provision of heatsinks on the printed circuit board or the use of cooling fans or other cooling methods might become necessary. Still, overheating of the printed circuit board (PCB) and /or the integrated circuits might occur, leading e.g. to mechanical tensions (and even, the breaking up or tearing apart of a soldering connection between a pin, and the PCB), and/or the destruction of an integrated circuit, etc., etc. With the ever increasing complexity and performance of integrated circuits, as well as the increasing component density on PCBs, more and more power/heat per PCB surface area is produced during their operation, increasing the problems.